Duchess difficult? In a shocking new interview, Meghan Markle’s former aide Samantha Cohen confirms that she was interviewed by Buckingham Palace about the royal’s reported mistreatment of staffers. In 2018, communications secretary Jason Knauf lodged a complaint against Meghan, accusing her of driving two personal assistants to quit and undermining the confidence of a third. Prince Harry’s wife, 42, was quick to deny the claims, but an investigation was launched — and while Samantha would not disclose what she told the palace, she did admit that finding someone to take over as Harry, 39, and Meghan’s private secretary was a struggle. “I was only supposed to stay for six months, but stayed for 18,” Samantha, 54, noted. “We couldn’t find a replacement for me, and when we did, we took…